The intracellular messenger cGMP is important for a wide variety of functions. It is generated by the enzyme guanylyl cyclase (GC). GCs exist in multiple forms and are classified as being either receptor (membrane associated) or soluble. Increases in the level of cGMP through the activation of GCs is thought to be important for the regulation of many different pathways with pathophysiological significance, including migraine, impotence, and asthma. cGMP is also involved in neuronal plasticity including LTP and LTD, adaptation at the level of the olfactory receptor neurons, and visual signal transduction among others. This application proposes to investigate the role of cGMP in the nervous system by examining the mechanisms of cGMP regulation in the olfactory system of Manduca sexta, an experimentally favorable model system in which the anatomy and electrophysiology are well studied. The studies described in this proposal will have significance for the understanding of the function of cGMP in the olfactory system, in the nervous system in general, and finally in any system in which cGMP plays a role in mediating cellular communication and function. The PI proposes to address the regulation of guanylyl cyclases in the olfactory system of Manduca sexta by answering the following questions as specific aims: (1) Which neurons in the antennal lobe can and do respond to NO? Nitric oxide (NO) is a potent stimulator of soluble GCs. (2) What is the function of the NO/sGC system in the antennal lobe? This specific aim examines the effects of pharmacological manipulation of the NO/sGC for either behavioral or electrophysiological outputs of the antennal lobe. (3) How is the activity of the function of the novel GC, MsGC-1, regulated in the olfactory system of Manduca sexta? MsGC-1 is a new type of GC whose expression pattern suggests that it plays an important role in the mediation of cGMP in the olfactory system. (4) What other GCs are expressed in the olfactory system of Manduca sexta? The PI has evidence of at least four more GCs expressed in the olfactory system. The PI proposes to clone these and examine their roles in mediating cGMP levels in the olfactory system.